1. The Field of the Invention
This invention pertains to multi-range synchronous shifting hydromechanical transmissions including steering transmissions wherein a gear train powered both by a mechanical input and the output of an infinitely variable device, e.g., a hydrostatic component also powered by the mechanical input, contains concentric gearing to supply various output combinations of the two inputs in distinct ranges, each range having a distinct torque ratio and wherein shifts between ranges are accomplished by relatively simultaneous activation of a brake or clutch controlling operation in one range and the deactivation of the brake or clutch controlling another range and wherein the hydrostatic component provides continuously variable drive ratios. More specifically, this invention pertains to hydromechanical transmissions wherein the gears forming the mechanisms to provide the distinct ranges are concentric in that they rotate about a common centerline so as to facilitate packaging of transmissions into a more compact form.
2. Description of the Prior Art
No all concentric, synchronous shifting hydromechanical transmission having three or more forward hydromechanical ranges or concentric gearbox for such transmission is known to Applicant other than that disclosed in this and the companion Application.
There are disclosures of concentric gear train hydromechanical transmissions or gear trains for such which have less than three forward ranges. These include the patents of Cockrell, U.S. Pat. No. 3,489,036, which is an all concentric, synchronous shifting truck transmission having a hydromechanical low/reverse range and a hydromechanical high range; Tipping, U.S. Pat. No. 3,752,010, which is also an all concentric truck transmission, having a hydrostatic low/reverse range combined with a hydromechanical high range; and Polak, U.S. Pat. No. 3,982,448, which discloses three models, two of which are all concentric truck transmissions having two forward ranges and one model which is not concentric in that it provides for an extra or third forward speed through the use of an additional shaft offset from the main axis. The transmission of W. A. Ross, U.S. Pat. No. 3,396,607, must be noted because to Applicant's knowledge it represents the only two forward range hydromechanical truck transmission in actual production. The transmission having a hydraulic component and a mechanical component, each on a separate shaft, is not concentric and includes a hydrostatic low/reverse range and a hydromechanical high range.
There are transmissions having three or more hydromechanical forward ranges which are neither all concentric nor contain a concentric gear train package. In this category are Tuck, U.S. Pat. No. 3,433,095, constituting a two axis non-concentric, three forward hydromechanical range transmission; and Nolan and Reed, U.S. Pat. No. 3,861,240, also constituting a two axis transmission having three hydromechanical forward ranges.
In addition, there are gear train packages or in some cases truck transmissions used with other components to constitute a steering transmission for track laying vehicles which have characteristics similar to some of the truck transmissions referred to above. An example is Polak, U.S. Pat. No. 3,596,535, wherein a full reversing mechanism and a differential "steer over" device have been superimposed on a truck transmission wherein the basic transmission gear train, although having a plurality of concentric planetary sets, depends on an additional shaft for the mechanical input to produce a hydrostatic low and a plurality of successively higher hydromechanical ranges. The Patents to Livezey, U.S. Pat. Nos. 3,575,066 and 3,583,256, are further examples of synchronous shifting multi-range steering transmissions similar in description to Polak, U.S. Pat. No. 3,596,535.
The transmission of Mooney et al, U.S. Pat. No. 3,777,593, most closely approaches the result obtained by the subject gear train and transmissions in that it contains an all concentric, synchronous shifting, multi-range truck transmission providing a hydrostatic low and two additional higher forward hydromechanical ranges wherein reverse gear is a part of the low range. This concentric transmission is, therefore, a three range transmission having one hydrostatic and two hydromechanical ranges based on two adjacent concentric planetary sets wherein one input is placed on both suns, one carrier is the output and is tied to the other ring. This is a fairly common combination of planetary sets (Simpson gear train) but Mooney by reversing the normal order of the two sets, inserting the second input by means of an axial shaft to the far side of the planetaries and using a drum to connect the "inside" planetary to output has obtained a very compact three range transmission that is concentric. However, Mooney's transmission is limited in flexibility and in range of torque output. The maximum torque used by Mooney is a sun to ring reduction from the hydrostatic input and it appears that the arrangement precludes a sun to carrier reduction. Speed is also limited as third gear is restricted to a range having the same slope as first/reverse and the total speed variation of first and reverse combined requires a trade-off between first range torque and total transmission speed range in a situation in which the total forward range of speed is already limited by use of one half of the range of the hydraulic motor in the first range for reverse. There is no possibility of adding additional ranges as all available combinations of the two inputs with the four elements of the two planetaries not connected to output have been used.